NONINVASIVE POSITIVE PRESSURE VENTILATION USING BILEVEL POSITIVE AIRWAY PRESSURE

Noninvasive Positive Pressure Ventilation (NIPPV) represents a cornerstone of modern respiratory support, offering a method to augment a patient’s breathing without the need for an endotracheal tube or tracheostomy. Among the primary modes of NIPPV is Bilevel Positive Airway Pressure (BiPAP), a sophisticated technique that delivers two distinct levels of pressure to assist both inhalation and exhalation. Its judicious application can significantly reduce the work of breathing, improve gas exchange, and, most critically, prevent the need for invasive mechanical ventilation and its associated complications.

Patient Selection and Key Indications

The success of BiPAP therapy is heavily dependent on appropriate patient selection. Not all patients in respiratory distress are suitable candidates. The decision to initiate BiPAP must be based on a careful assessment of the underlying pathophysiology and the patient’s clinical status.

Primary Indications with Strong Evidence:

1. Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: This is the most well-established indication for BiPAP. In COPD patients with acute hypercapnic respiratory failure (elevated PaCO2 and respiratory acidosis), BiPAP works by reducing the work of breathing, splinting open small airways that would otherwise collapse on expiration, and increasing tidal volume to improve ventilation and “blow off” excess CO2. It has been shown to reduce intubation rates, hospital length of stay, and mortality (Liesching, Kwok, & Hill, 2003).
2. Cardiogenic Pulmonary Edema (CPE): For patients with acute respiratory failure from CPE, BiPAP provides dual benefits. The expiratory pressure (EPAP) acts like Positive End-Expiratory Pressure (PEEP), increasing intrathoracic pressure, which reduces venous return to the heart (preload) and decreases the pressure the left ventricle must pump against (afterload). This combined effect alleviates pulmonary congestion while improving oxygenation by recruiting fluid-filled alveoli (Masip et al., 2005).
3. Acute Hypoxemic Respiratory Failure in Immunocompromised Patients: In this vulnerable population, avoiding intubation is paramount due to the high risk of ventilator-associated pneumonia (VAP) and other nosocomial infections. BiPAP can serve as a bridge, providing necessary respiratory support while underlying conditions (e.g., opportunistic infections) are treated.
4. Post-Extubation Respiratory Support: For certain high-risk patients, BiPAP can be used immediately after extubation to prevent re-intubation by staving off respiratory muscle fatigue and maintaining airway patency.
5. Palliative Care: In patients with “Do Not Intubate” (DNI) orders, BiPAP can be a powerful tool to alleviate dyspnea and provide comfort during end-of-life care.

Identifying Contraindications and Cautions

Equally important to knowing when to use BiPAP is knowing when not to. Applying BiPAP to an inappropriate candidate can lead to significant harm, including aspiration, delayed intubation, and clinical deterioration.

Absolute Contraindications:

• Respiratory or Cardiac Arrest: These situations require immediate intubation and invasive ventilation.
• Inability to Protect Airway: Patients who are comatose, have a severely impaired gag reflex, or are experiencing uncontrollable vomiting are at extremely high risk for aspiration.
• Copious Secretions or Inability to Clear Secretions: The positive pressure can force secretions deeper into the lungs, and the mask interface prevents effective suctioning.
• Severe Facial Trauma, Burns, or Recent Upper Airway/Esophageal Surgery: A proper mask seal is impossible, and positive pressure may compromise surgical anastomoses.
• Hemodynamic Instability or Life-Threatening Arrhythmias: The increased intrathoracic pressure from BiPAP can reduce preload and worsen hypotension.

Relative Contraindications (Proceed with Extreme Caution):

• Agitated or uncooperative patient
• High aspiration risk (e.g., active upper GI bleed)
• Anatomic facial abnormalities preventing a good mask seal

Equipment Preparation and Setup

Proper setup is essential for effective therapy and patient comfort. The core components include:

1. The Ventilator: A portable or ICU-grade ventilator capable of delivering bilevel pressure.
2. The Circuit: Standard, single-limb ventilator tubing. It is crucial to ensure the exhalation port (either built into the mask or as a separate valve in the circuit) is unobstructed to prevent CO2 rebreathing.
3. The Interface (Mask): The choice of mask is critical.
   • Oronasal (Full-Face) Mask: Covers both the nose and mouth. It is the most common choice in the acute setting as it compensates for mouth breathing but has a higher risk of aspiration and claustrophobia.
   • Nasal Mask: Covers only the nose. Better tolerated and allows for speaking/eating, but less effective if the patient is a mouth breather.
   • Nasal Pillows: Small prongs that insert into the nares. Primarily used for chronic, home-based therapy.
4. Humidification: A heated humidifier should be integrated into the circuit to warm and moisten the inspired air. This improves patient comfort, prevents mucosal drying, and aids in secretion mobilization.
5. Oxygen Source: The ventilator is connected to an oxygen source to allow for titration of the fraction of inspired oxygen (FiO2).

Initiating Therapy and Setting Parameters

Once the patient is deemed a suitable candidate and the equipment is ready, therapy can be initiated. A calm and reassuring approach is vital to gain patient cooperation.

1. Patient Positioning: Sit the patient upright (at least 45 degrees) to maximize lung expansion and reduce the risk of aspiration.
2. Explanation: Clearly explain the procedure, the sensation of the pressure, and the importance of synchronizing their breathing with the machine.
3. Initial Application: Start by holding the mask gently over the patient’s face without the straps, using low-pressure settings. This allows the patient to acclimate to the sensation.
4. Securing the Mask: Once the patient is comfortable, secure the straps. The fit should be snug enough to minimize leaks but not so tight as to cause pressure sores.

Initial Settings:

• IPAP (Inspiratory Positive Airway Pressure): This higher pressure is delivered during inspiration to augment the patient’s breath, increase tidal volume, and reduce the work of breathing. A typical starting setting is 8-12 cm H2O.
• EPAP (Expiratory Positive Airway Pressure): This lower pressure is maintained during exhalation to keep the airways open (acting as PEEP), improve oxygenation by recruiting alveoli, and counter auto-PEEP in COPD patients. A typical starting setting is 4-6 cm H2O.
• Pressure Support (PS): The difference between IPAP and EPAP (IPAP – EPAP). This gradient is the primary determinant of ventilation and CO2 clearance. The initial PS is usually 4-6 cm H2O.
• FiO2: Start with a setting sufficient to maintain an oxygen saturation (SpO2) >90-92% and titrate as needed.
• Backup Rate: Set a backup respiratory rate (e.g., 10-12 breaths/min) as a safety measure in case the patient becomes apneic or their respiratory drive diminishes.

Monitoring, Titration, and Troubleshooting

BiPAP is not a “set it and forget it” therapy. Continuous monitoring and adjustment are key to success.

Monitoring:

• Clinical: Observe the patient’s respiratory rate, work of breathing (accessory muscle use), heart rate, blood pressure, and mental status. Improvement is often seen within the first 1-2 hours.
• Objective: Continuously monitor SpO2. An arterial blood gas (ABG) should be obtained 1-2 hours after initiation to assess for changes in pH, PaCO2, and PaO2.
• Ventilator Data: Monitor for air leaks, patient-ventilator synchrony, and delivered tidal volumes.

Titration:

• For Hypercapnia (High PaCO2): To improve ventilation and blow off CO2, increase the pressure support gradient. This is typically done by increasing the IPAP in increments of 2 cm H2O (e.g., from 12/5 to 14/5).
• For Hypoxemia (Low PaO2): To improve oxygenation, increase the EPAP and/or the FiO2. Increasing EPAP helps recruit more alveoli for gas exchange.
• For Patient Comfort: Adjust rise time and cycle sensitivity settings if the patient appears to be fighting the ventilator.

Troubleshooting Common Issues:

• Air Leaks: Re-adjust the mask and headgear. If persistent, consider changing the mask size or type.
• Patient Anxiety/Claustrophobia: Provide reassurance. A short break or a low-dose anxiolytic may be necessary.
• Gastric Insufflation: This occurs when air is forced into the stomach. It can be mitigated by keeping IPAP pressures below 20 cm H2O and maintaining an upright position.
• Skin Breakdown: Prophylactically apply skin barriers or hydrocolloid dressings to the nasal bridge and other pressure points.

Weaning and Discontinuation

The goal of BiPAP is to serve as a temporary bridge. Weaning should be considered once the underlying cause of respiratory failure is improving and the patient is clinically stable.

1. Assess for Readiness: The patient should have a stable respiratory rate (<25/min), improved gas exchange, and minimal signs of respiratory distress.
2. Gradual Reduction: Begin by slowly decreasing the pressure support (lowering IPAP) and FiO2 while monitoring the patient’s response.
3. Trial Periods: Initiate planned “breaks” from BiPAP, starting with 30-60 minutes and gradually increasing the duration as tolerated. The patient should be monitored closely for any signs of fatigue or decompensation during these off-periods.
4. Discontinuation: Therapy can be fully discontinued once the patient can comfortably maintain adequate gas exchange and respiratory status without support.

In conclusion, BiPAP is a powerful and efficacious modality in the management of acute respiratory failure. Its success hinges upon a systematic approach encompassing careful patient selection, meticulous setup and application, vigilant monitoring, and dynamic titration. When used correctly, it stands as a life-saving intervention that can effectively bridge patients through critical illness while avoiding the significant morbidity associated with invasive mechanical ventilation.

References

1. Keenan, S. P., Sinuff, T., Burns, K. E., et al. (2011). Clinical practice guidelines for the use of noninvasive positive-pressure ventilation and noninvasive continuous positive airway pressure in the acute care setting. CMAJ : Canadian Medical Association Journal, 183(3), E195–E214.
2. Liesching, T., Kwok, H., & Hill, N. S. (2003). Acute applications of noninvasive positive pressure ventilation. Chest, 124(2), 699–713.
3. Masip, J., Roque, M., Sánchez, B., Fernández, R., & Subirana, M. (2005). Noninvasive ventilation in acute cardiogenic pulmonary edema: systematic review and meta-analysis. JAMA, 294(24), 3124–3130.
4. Rochwerg, B., Brochard, L., Elliott, M. W., et al. (2017). Official ERS/ATS clinical practice guidelines: noninvasive ventilation for acute respiratory failure. European Respiratory Journal, 50(2), 1602426.